ChemFiles Volume 5 Article 10

Another goal that Pd catalysts must achieve before industrial applications can be realized involves the recovery and reuse of the catalyst, because homogeneous palladium catalysts contaminate products, process equipment, and waste streams necessitating costly clean-up procedures. Furthermore, the loss of catalyst during the reaction and reaction work-up limits catalyst activity (TONs) and has proven to be cost prohibitive with respect to process scale. Sigma-Aldrich has addressed these issues by offering Pd EnCat™ catalysts, wherein the metal is microencapsulated within a polyurea matrix thereby preventing Pd leaching. The advantage of Pd EnCat™ catalysts are numerous: 1) low, residual metal levels in crude product (usually <10 ppm before purification); 2) easy recovery of catalyst; 3) compatability of immobilized metal with various ligands to effect C–C bond forming reactions; 4) safer and easier to handle than Pd/C for hydrogenation; and 5) efficiency and economy gains through recovery and recycling. The range of processes mediated by Pd EnCat™ catalysts is well documented including Suzuki, Heck, carbonylation, and Stille couplings, to reductions of carbonyls, alkenes, and epoxides via hydrogenation (Scheme 15). Sigma-Aldrich carries a full line of Pd EnCat™ catalysts licensed through Reaxa and available with co-encapsulated phosphine ligands, thereby facilitating the removal of Pd metal and the ligand.

Scheme 15

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